The present invention relates to a method and device for automatically controlling welding conditions for use in an arc welding machine.
When a steel plate is welded by an arc or electric welding, in order to obtain the best welding result, conditions such as welding voltage, welding current, welding speed, and so forth, are properly set up.
When such welding conditions are changed in the course of the welding operation, for example, on the conditions 19 V.times.100 A between the points A and B, and 20 V.times.130 A between the points B and C, these conditions between the points A and C are readily stored in a memory. However, the following problems are raised when the welding operation is carried out.
Although the setup of the welding conditions of generally used welding machines is somewhat different in detail depending on their manufacturers, however, it is basically the same, and is carried out as follows.
(1) The welding voltage adjustment:
A dial of a potentiometer of a remote controller is turned to change a voltage.
An ignition or turn-on phase of a thyristor is changed according to the voltage change.
The output direct voltage for welding is changed.
(2) The welding current adjustment:
A dial of a potentiometer of a remote controller is turned to change a voltage.
An ignition or turn-on phase of a thyristor is changed according to the voltage change.
The rotation number of a motor for feeding a welding rod or wire is changed.
The feeding speed of the welding rod of wire is changed.
The welding current is changed.
FIG. 1 shows simply a conventional voltage control circuit A for a conventional arc or electric welding machine generally used, which comprises a remote control part 1 including a potentiometer VR.sub.1 for adjusting a voltage, a welding control part 2, and a connection cable 3 which couples the two parts 1 and 2. The welding control part 2 comprises a conventional voltage regulator 4, half-fixed potentiometer VR.sub.2 and VR.sub.3 which determine the upper and the lower limits of the output voltage, and a phase controller 5 which controls a main thyristor (not shown).
A fixed voltage is supplied to both the terminals of the potentiometer VR.sub.1 from the voltage regulator 4, and thus, when the potentiometer VR.sub.1 is turned, the input voltage of the phase controller 5 is varied, with the result that the phase of the output pulse is varied.
Therefore, when the potentiometer VR.sub.1 is turned, the output voltage of the main thyristor, i.e. the output voltage of the welding machine, is changed. Accordingly, in order to change the welding voltage during the welding operation, the potentiometer VR.sub.1 is turned by means of a motor depending on data read out of the memory. That is, the reconstruction of the remote control part 1 is required accordingly.
The welding current control can be carried out by utilizing the phase controller together with the thyristor, and the potentiometer in the same manner as described above.
Meanwhile, the action of the thyristor can directly be controlled by the output of the memory, but this method involves the reconstruction of the welding machine.
In the embodiments described above, the reconstruction of the welding machine or the change of the control circuit of the same, or a particularly specified welding machine for exclusive use is required, which is not preferable nor recommendable and requires often high cost.